1. Field of the Invention
This invention relates generally to apparatus and methods that utilize an "ice-on-coil" (IOC) thermal storage technique, as opposed to other methods of thermal storage, and more particularly to ice thermal storage coil systems and methods for use in "ice-on-coil" (IOC) installations.
2. Brief Description of the Prior Art
Current "ice-on-coil" (IOC) thermal storage methods use either coils formed of plastic tubes or galvanized steel tubes in bundled modules. Major suppliers of IOC thermal storage systems include: Baltimore Aircoil Co. of Jessup, Md., Evapco, Inc. of Westminster, Md. (steel tubes), Calmac Manufacturing Corp. of Englewood, N.J., and Fafco, Inc. of Redwood City, Calif. (plastic tubes). The art of each involves methods of circuiting the coil modules to best achieve even ice-build and melt processes, and to best manage the air removal during glycol-filling and draining processes. However, each has major draw-backs which are difficult to manage economically when projected to the larger capacity systems where many modules are connected in parallel or installed in deep tanks where it is desired to minimize the floor space used for the water-filled storage tanks which contain the coil modules. These state-of-the-art systems require massive welded piping and manifolds below the waterline of the ice storage tanks to facilitate piping connections to each module of the stacked module groupings and to achieve the reverse-piping arrangements to successfully remove air during filling with the glycol-water refrigerant inside the coil tubes.
FIG. 1 is an example of a typical serpentine "ice-on-coil" system of the current state-of-the-art, or prior art. As shown in FIG. 1, the serpentine coil modules are at least 2 times as wide as they are high. In the real applications of these prior art coils, the serpentines are typically up to 7' high by 21' wide per module. Some are even less than 7' high by 21' wide, and in the case of smaller prior art coil modules, the units are typically 4' high by 12' wide.
The prior art typically uses a stack of two to six deep coil modules, and presents many problems during construction to actually provide a space sufficient to complete the piping installation with suitable access space for welders down deep in the tank between the coil modules. This welding access and lost piping space also requires the tank to be larger than required. The present invention eliminates the major problem of tight working spaces for welding the manifold connections and piping in the deep tanks and allows use of a smaller tank for the same total thermal storage capacity requirement.
Prior art steel tubes used for the coils are typically welded on-line as they are manufactured by roll-forming from thin strips of sheet steel. These tubes are then formed to about 180 degree U-bends as they make up a serpentine, then the serpentines are stacked in a spaced frame to form a complete coil module and are further welded at the tube ends to a drilled or punched header plate. The header plates are then enclosed by a welded channel to form a closed manifold for the inlet or outlet connections of the coil module. The coil tubes are more likely to leak at the field piping or header joints than any other area, even after galvanizing. The present invention provides an accessible tube option to isolate as few as two tubes at the top, without losing any significant ice-making capacity, should a leak occur in a tube circuit.
The present invention is distinguished over the prior art in general, by an ice-on-coil (IOC) thermal storage coil system and method utilizing "deep-tank" technology and dimensional relationship of coil height to coil width wherein the coil serpentine's height (vertical tube dimension) is greater than the width (the horizontal dimension), and wherein all manifold and header joints are above, or just below the water surface of the tank, easily visible and accessible for maintenance, assembly, leak-checking or repair. Another aspect of the present ice-on-coil (IOC) thermal storage coil system and method is that, in some embodiments, the ice-coil tubes are never horizontal anywhere in the full coil height, but instead vertical tubes or "near-horizontal" sloped tubes are utilized which slope in an upward direction to facilitate air removal during filling of the coil with the coolant mixture.